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.Dd January 4, 2012
.Dt IPSEC_SET_POLICY 3
.Os
.Sh NAME
.Nm ipsec_set_policy ,
.Nm ipsec_get_policylen ,
.Nm ipsec_dump_policy
.Nd manipulate IPsec policy specification structure from human-readable policy string
.\"
.Sh LIBRARY
.Lb libipsec
.Sh SYNOPSIS
.In netipsec/ipsec.h
.Ft "char *"
.Fn ipsec_set_policy "const char *policy" "int len"
.Ft int
.Fn ipsec_get_policylen "char *buf"
.Ft "char *"
.Fn ipsec_dump_policy "char *buf" "const char *delim"
.Sh DESCRIPTION
.Fn ipsec_set_policy
generates an IPsec policy specification structure, namely
.Li struct sadb_x_policy
and/or
.Li struct sadb_x_ipsecrequest
from a human-readable policy specification.
The policy specification must be given as a C string
.Fa policy
and its length
.Fa len .
.Fn ipsec_set_policy
will return a buffer with the corresponding IPsec policy specification structure.
The buffer is dynamically allocated, and must be
.Xr free 3 Ap d
by the caller.
.Pp
You can get the length of the generated buffer with
.Fn ipsec_get_policylen
(i.e. for calling
.Xr setsockopt 2 ) .
.Pp
.Fn ipsec_dump_policy
converts an IPsec policy structure into human-readable form.
Therefore,
.Fn ipsec_dump_policy
can be regarded as the inverse function to
.Fn ipsec_set_policy .
.Fa buf
points to an IPsec policy structure,
.Li struct sadb_x_policy .
.Fa delim
is a delimiter string, which is usually a blank character.
If you set
.Fa delim
to
.Dv NULL ,
a single whitespace is assumed.
.Fn ipsec_dump_policy
returns a pointer to a dynamically allocated string.
It is the caller's responsibility to
.Xr free 3
it.
.Pp
.Fa policy
is formatted as either of the following:
.Bl -tag  -width "discard"
.It Ar direction [priority specification] Li discard
.Ar direction
must be
.Li in ,
.Li out ,
or
.Li fwd .
.Ar direction
specifies in which direction the policy needs to be applied.
The non-standard direction
.Li fwd
is substituted with
.Li in
on platforms which do not support forward policies.
.Pp
.Ar priority specification
is used to control the placement of the policy within the SPD.
The policy position is determined by
a signed integer where higher priorities indicate the policy is placed
closer to the beginning of the list and lower priorities indicate the
policy is placed closer to the end of the list.
Policies with equal
priorities are added at the end of the group of such policies.
.Pp
Priority can only
be specified when libipsec has been compiled against kernel headers that
support policy priorities (Linux \*[Gt]= 2.6.6).
It takes one of the following formats:
.Bl -tag  -width "discard"
.It Ar {priority,prio} offset
.Ar offset
is an integer in the range \-2147483647..214783648.
.It Ar {priority,prio} base {+,-} offset
.Ar base
is either
.Li low (-1073741824) ,
.Li def (0) ,
or
.Li high (1073741824) .
.Pp
.Ar offset
is an unsigned integer.
It can be up to 1073741824 for
positive offsets, and up to 1073741823 for negative offsets.
.El
.Pp
The interpretation of policy priority in these functions and the
kernel DOES differ.
The relationship between the two can be described as
p(kernel) = 0x80000000 - p(func)
.Pp
With
.Li discard
policy, packets will be dropped if they match the policy.
.It Ar direction [priority specification] Li entrust
.Li entrust
means to consult the SPD defined by
.Xr setkey 8 .
.It Ar direction [priority specification] Li bypass
.Li bypass
means to bypass the IPsec processing.
.Pq the packet will be transmitted in clear .
This is for privileged sockets.
.It Ar direction Bo Ar priority specification Bc Li ipsec Ar request ...
.Li ipsec
means that the matching packets are subject to IPsec processing.
.Li ipsec
can be followed by one or more
.Ar request
strings, which are formatted as below:
.Bl -tag  -width "discard"
.It Ar protocol Li / Ar mode Li / Ar src Li - Ar dst Op Ar /level
.Ar protocol
is either
.Li ah ,
.Li esp ,
or
.Li ipcomp .
.Pp
.Ar mode
is either
.Li transport
or
.Li tunnel .
.Pp
.Ar src
and
.Ar dst
specifies the IPsec endpoint.
.Ar src
always means the
.Dq sending node
and
.Ar dst
always means the
.Dq receiving node .
Therefore, when
.Ar direction
is
.Li in ,
.Ar dst
is this node
and
.Ar src
is the other node
.Pq peer .
If
.Ar mode
is
.Li transport ,
Both
.Ar src
and
.Ar dst
can be omitted.
.Pp
.Ar level
must be set to one of the following:
.Li default , use , require ,
or
.Li unique .
.Li default
means that the kernel should consult the system default policy
defined by
.Xr sysctl 8 ,
such as
.Li net.inet.ipsec.esp_trans_deflev .
See
.Xr ipsec 4
regarding the system default.
.Li use
means that a relevant SA can be used when available,
since the kernel may perform IPsec operation against packets when possible.
In this case, packets can be transmitted in clear
.Pq when SA is not available ,
or encrypted
.Pq when SA is available .
.Li require
means that a relevant SA is required,
since the kernel must perform IPsec operation against packets.
.Li unique
is the same as
.Li require ,
but adds the restriction that the SA for outbound traffic is used
only for this policy.
You may need the identifier in order to relate the policy and the SA
when you define the SA by manual keying.
You can put the decimal number as the identifier after
.Li unique
like
.Li unique : number .
.Li number
must be between 1 and 32767 .
If the
.Ar request
string is kept unambiguous,
.Ar level
and slash prior to
.Ar level
can be omitted.
However, it is encouraged to specify them explicitly
to avoid unintended behavior.
If
.Ar level
is omitted, it will be interpreted as
.Li default .
.El
.Pp
Note that there are slight differences to the specification of
.Xr setkey 8 .
In the specification of
.Xr setkey 8 ,
both
.Li entrust
and
.Li bypass
are not used.
Refer to
.Xr setkey 8
for details.
.Pp
Here are several examples
.Pq long lines are wrapped for readability :
.Bd -literal -offset indent
in discard
out ipsec esp/transport//require
in ipsec ah/transport//require
out ipsec esp/tunnel/10.1.1.2-10.1.1.1/use
in ipsec ipcomp/transport//use
        esp/transport//use
.Ed
.El
.Sh RETURN VALUES
.Fn ipsec_set_policy
returns a pointer to the allocated buffer with the policy specification
if successful; otherwise a
.Dv NULL
pointer is returned.
.Fn ipsec_get_policylen
returns a positive value
.Pq meaning the buffer size
on success, and a negative value on errors.
.Fn ipsec_dump_policy
returns a pointer to a dynamically allocated region on success,
and
.Dv NULL
on errors.
.Sh SEE ALSO
.Xr ipsec_strerror 3 ,
.Xr ipsec 4 ,
.Xr setkey 8
.Sh HISTORY
The functions first appeared in the WIDE/KAME IPv6 protocol stack kit.
